Switching mechanism

ABSTRACT

THE FOLLOWING SPECIFICATION DESCRIBERS A SWITCH IN WHICH ONE OR MORE CONDUCTIVE TRANSMISSION BARS ARE CONNECTABLE TO AN INPUT TERMINAL AND ONE OR MORE DISCRETE, CONDUCTIVE RECEIVING STRIPS ARE EACH CONNECTABLE TO AN OUTPUT TERMINAL. THE INPUT TERMINAL IS INTENDED TO BE CONNECTED TO A SOURCE OF A SIGNAL OF CHANGING POTENTIAL, AND IN ONE FORM IS CONNECTABE TO THE TRANSMISSION BARS BY A COMMUTATING DEVICE. IN SUCH CASE, A SINGLE LARGE RECEIVING STRIP CAN BE USED DIRECTLY CONNECTED TO THE OUTPUT TERMINAL. IN ANOTHER FORM, THE INPUT TERMINAL IS DIRECTLY CONNECTED TO A SINGLE TRANSMISSION BAR AND A NUMBER OF RECEIVING STRIPS ARE CONNECTABLE THROUGH COMMUTATION TO THE OUTPUT TERMINAL. A MANUALLY ENGAGEABLE KEY IN THE FORM OF AN ELECTROSTATIC SHIELDING ELEMENT IS NORMALLY INTERPOSED BETWEEN THE TRANSMISSION AND RECEIVING ELEMENTS SO AS TO PREVENT CAPACITIVE COUPLING OF THE SIGNAL FROM OCCURRING BETWEEN THE TRANSMISSION AND RECEIVING ELEMENTS. THE KEY IS MOVABLE TO A POSITION AT WHICH APERTURES IN THE KEY PERMIT COUPLING AND THUS SWITCHING TO OCCUR. THE KEY CAN, BE VIRTUE OF THE NUMBER AND PLCEMENT OF APERTURES IN IT, DIRECTLY ENCODE THE SIGNAL INTO A GIVEN NUMERIAL FORM DEFINED BY SELECTIVE ENERGIZATION OF THE INPUT TERMINALS, AND HENCE FORMS A BASIC ELEMENT FOR A MULTIPLE KEY KEYBOARD.

D. C. GQVE SWITCHING MECHANISM Feb. 16, 1971 2 Sheets-Sheet 1 Filed Dec.16, 1968 DONALD a GUI/E INVENTOR.

BY Sm ATTORNEY Feb. 16, 1971 D V 3,564,541

SWITCHING MECHANISM Filed Dec. 16, 1968 2 Sheets-Sheet 2 SHIFT AREGISTER SHIFT CONDITION REGISTER CONDITION W IIIIAIIIII I ,IIIL

.r F G! E; A

DONALD C GUI/E IINVENTOR.

RM} S I ATTORNEY COMM - COMM.

OSC.

FIG. 7.

United States Patent Int. Cl. -G08c 9/02 US. Cl. 340365 6 ClaimsABSTRACT OF THE DISCLOSURE The following specification describes aswitch in which one or more conductive transmission bars are connectableto an input terminal and one or more discrete, conductive receivingstrips are each connectable to an output terminal. The input terminal isintended to be connected to a source of a signal of changing potential,and in one form is connectable to the transmission bars by a commutatingdevice. In such case, a single large receiving stri can be used directlyconnected to the output terminal. In another form, the input terminal isdirectly connected to a single transmission bar and a number ofreceiving strips are connectable through commutation to the outputterminal. A manually engageable key in the form of an electrostaticshielding element is normally interposed between the transmission andreceiving elements so as to prevent capacitive coupling of the signalfrom occurring between the transmission and receiving elements. The keyis movable to a position at which apertures in the key permit couplingand thus switching to occur. The key can, by virtue of the number andplacement of apertures in it, directly encode the signal into a givennumerical form defined by selective energization of the input terminals,and hence forms a basic element for a multiple key keyboard.

This application is a continuation-in-part of copending application Ser.No. 607,563 filed Jan. 5, 1967 now U.S. Pat. 3,419,697.

This invention relates to an electrical switching device and moreparticularly to novel switching means adapted for multiple keyboardswitching.

As is well known, the typical electronic calculator operates on thebasis of a numerical or logical system other than decimal because of thedifficulty in manipulating decimal notation or multivalued logic.However, because data is most generally in decimal form, a manuallymanipulated input key-board to a calculator is usually designed toaccept information in decimal terms. Hence, the device usually requiresmeans for coding the decimal input data into another numerical system(typically binary) more suited for machine usage.

A usual input keyboard comprises a plurality of keys, each connected tooperate a mechanical switch. The state of the keyboard switches isconverted to an appropriately coded signal either by using cross-barswitches in which the coding is directly accomplished, or by usingsimple mechanical switches with auxiliary apparatus such as a diodematrix to achieve coding. The portion of the mechanical switch movedmanually usually is a currentcarrying element, hence the latter must beinsulated so that the operator is not exposed to the current. Of course,in either type of switch there are a number of other problems posed byits mechanical construction. For example, mechanical contact switchingtends to be noisy, being subject to switching transients and contactbounce. Mechanical contact switches also tend to Wear at the contactsurfaces and hence have limited life and reliability.

The present invention, therefore, has as a principal ice object theprovision of novel switching means particularly adapted to providesignal encoding Without the above noted problems characteristic ofmechanical contact switches.

Another object of the present invention is to provide switching means'with increased reliability because switching is achieved substantiallywithout contact arcing, bounce, or wear.

Yet another object of the present invention is to achieve directencoding of a value into serial form Without employing diode matrices orthe like. Briefly, to accomplish these and other objects, the presentinvention is embodied in a three-element switch intended to switch onlychanging potentials. The switch comprises a first element having asignal transmitting surface, a second element having a signal receivingsurface, the two elements being disposed so that an interspace isprovided between the twofacing surfaces. The third element is anelectrically conductive electrostatic shield disposed between thereceiving and transmitting surfaces. It will be apparent that when thefirst element is connected to a source of changing potential, thepresence of an electrostatic shield between the receiving andtransmitting surfaces will prevent the occurrence of any capacitivecoupling of the signal at the transmitting surface with the receivingsurface. Therefore,

the shield has a configuration such that a portion thereof is notelectrically conductive but presents a dielectric aperture through whichcapacitive coupling of respective surfaces can be achieved. At least oneof the elements is movable with respect to the others so that couplingis effected only in a predetermined relative position of the threeelements and preferably in no other position. Thus, the output of theswitch is uniquely related to the nature and position of transmittingand receiving surfaces and dielectric apertures so that direct coding bythe switch is readily accomplished. Where the transmission surfaces areall simultaneously enerigized, the output is a parallel coded signal. Asystem of this type, disclosed in said copending application, thereforewould normally require a multiplicity of signal conditioners such asamplifiers, drivers and the like for each switch.

However, often it is desirable to provide the output code in serialrather than parallel form. Such a serial system requires, of course, butone output channel requiring but a single signal conditioning means. Thepresent invention is therefore an improvement on the aforesaid codingsystem in that it inherently provides serial rather than parallelencoding.

Other objects of the invention will in part be obvious and will in partappear hereinafter. The invention accordingly comprises the apparatuspossessing the construction, combination of elements, and arrangement ofparts which are exemplified in the following detailed-disclosure, andthe scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the presentinvention, reference should be had to the following detailed descriptiontaken in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic perspective view partly in fragment of anassembled switch embodying the principles of the present invention FIG.2 is an exploded perspective showing the relation and details of anumber of the elements of the switch of FIG. 1;

FIG. 3 is a partial cross-section of a portion of the embodiment of FIG.1 taken along the line 33;

FIG. 4 is a schematic perspective view showing the relation of a numberof selected elements of the embodiment of FIG. 1 when the switch is in aconducting position;

FIG. 5 is a schematic representation showing the elements of FIG. 4 whenthe switch is in a non-conducting position;

FIG. 6 is a schematic circuit diagram, partly in block form, showing anembodiment of the present invention useful for multiple signal encoding,and

FIG. 7 is yet another schematic circuit diagram, partly in block form,showing another signal encoding system.

As previously noted, the switching means of the present invention isintended to connect input and output terminals through a capacitivecoupling phenomenon, and hence requires that the signal at the inputterminal be a changing potential, i.e., a smoothly changing potential,such as an oscillating Voltage, or a step-change such as is found with apulse train input or the like.

Referring now to FIGS. 1-3, there is shown one embodiment of the presentinvention comprising reception element having at least one elongatedslab 22 of an electrically conductive material such as copper or thelike. One surface of the slab bears an electrically insulating element24, for example of an enamel or other dielectric material. Another thinlayer of electrically conductive material 26 overlies insulating layer24. One or more areas of slab 22 are devoid of both layers 24 and 26such that there is at least one discrete, exposed, uninsulated surfaceportion 28 of the electrically-conductive material of slab 22, Le. anaperture through to the layers 24 and 26. Where there are more than oneuninsulated portion 28, each such surface portion is spaced apart andseparated from the others by the presence of the intervening structureof layers 24 and 26. Obviously, all uninsulated surface portions 28 areelectrically connected to one another through the body of slab 22.Means, such as lead 29, are provided for connecting slab 22 to an outputterminal. Layer 26 is preferably connected to a system ground and henceprovides electrostatic shielding with respect to the other areas of thesurface of slab 22, directly underlying layer 26.

Spaced from element 20 is transmission element 30 which typicallycomprises elongated support means in the form of insulating substrate32, for example of glass or glass-epoxy resin. Mounted on a surface ofsubstrate 32 so as to be in register with each surface portion 28 (i.e.,in facing relation across the interspace between transmission element 20and reception element 30) is a corresponding, electrically-conductiveelement, for example flat metallic strip 34. If more than one such stripis required because there is more than one surface portion 28, thestrips are spaced from one another and are held electrically insulatedfrom one another by substrate 32.

In a preferred embodiment, elements 20 and 30 are fixedly mounted withrespect to one another so that each surface portion 28 is in fixedregister with a corresponding strip 34. Mounted for movement between andspaced from both elements 20 and 30 is electrostatic shielding means 36preferably formed of an electrically-conductive material and having atleast one aperture 38 therein. Aperture 38 can simply be a hole whichcontains a dielectric material such as a vacuum, air or even a soliddielectric, as desired. Where the facing surfaces of the transmissionand reception elements are substantially planar, the electrostaticshield can simply be a flat metallic plate with one or more apertures 38appropriately placed, as will appear hereinafter.

Shielding means 36 is preferably mounted for movement within theinterspace between elements 20 and 30* such that in a unique position ofthe shield, every aperture 38 lies between a corresponding registeredpair of a surface portion 28 and a strip 34, thereby permitting anychanging potential on the latter to be capacitively coupled to itsregistered portion 28. Preferably, in all other positions to which theshield is movable, the electricallyconductive material of the shield isinterposed between the registered pair or pairs. Because shielding means36 is also connected to ground, it is apparent that it will constitutean electrostatic shield preventing capacitive coupling when interposedbetween a registered pair.

A switch of the present invention, particularly adapted for use as akeyboard switch, is as shown in FIGS. 1 and 2 wherein reception element20 is a slab formed in a U-shape such that the surface bearing layers 24and 26 is on the outside of the U. Element 20 is fixedly mounted at thebase of the U upon a support such as plate 40. As shown in FIG. 2, anumber of surface portions 28 are provided as perforations extendingthrough layers 24and 26 to expose the electrically conductive materialof slab 22. It will be recognized that because of the U- shape ofelement 20, there are two outwardly facing surfaces, each of which maybear one or more surface portions 28. Consequently, opposite each arm ofthe U-shape of element 20' is a corresponding transmission element 30provided with a plurality of strips 34. For each surface portion 28 ofelement 20 there is at least one registered corresponding strip 34. Eachof the elements 30 is also fixedly mounted on base 40 in properrelationship to the outwardly facing surfaces of element 20.

The switch of FIGS. 1 and 2 also includes electrostatic shielding means36 in the form of a metallic strip bent to form a U, dimensioned so asto fit outside element 20 but inside the interspace between element 20and ele ment 30. Element 36 is mounted for movement within theinterspace between element 20 and element 30 in the following manner:there is provided top plate 42 having a central aperture 43 into whichshielding means 36 is slidably mounted. Means (not shown) are includedfor mounting plate 42 in a substantially fixed, parallel relation withplate 40. Rigidly mounted on the inside of the base of the U-shape ofmeans 36 and extending substantially centrally between and parallel tothe arms of the U-shape thereof is pin 44. Slidably mounted on pin 44 isbar 46 which extends substantially perpendicularly to pin 44 and isdimensioned to be longer than the width of shielding means 36, and,therefore, extends outwardly from the bight of the U-shape of the latterso as to be engageable with edge portions of the periphery of aperture43 in plate 42. Resilient means such as spring 48 is mounted about pin44, one end of spring 48 being anchored at the distal end of the pin,the other end of spring 48 being anchored on bar 46 adjacent the pin.Manually engageable button 50, typically intended to bear on its topsurface a numerical or other indicium, is affixed to the outside of thebase of the U-shape of shielding means 36.

As shown assembled in FIG. 1, when shielding means 36 is positioned inaperture 43 of plate 42 such that bar 46 engages the top surface ofplate 42, spring 48 serves to retain shielding means 36 in a normalposition wherein (as schematically shown in FIG. 5 apertures 38 inshielding means 36 are completely out of alignment with any registeredsurface portion 28 and strip 34. In this normal position of theshielding means, the electrically conductive body of the shield isinterposed between each registered pair of surface portions 28 andstrips 34. When button 50 is subjected to manual pressure so as to forcethe shield to move downwardly through the interspace between elements 20and 30, because one end of spring 48 is fixedly positioned by theengagement of bar 46 and plate 42, the other end of the spring moveswith pin 44, and the spring is placed under tension. Of course, uponrelease of pressure on button 50, the spring will tend to restoreshielding means 36 to its normal position.

For convenience in manufacture, each of transmission elements 30 ispreferably provided in an embodiment such as that shown in FIGS. 1 and2, wherein each element 30 has the same plurality of strips 34 thereon,each strip corresponding for example to a specific whole power of aradix of a numerical code. Thus, as shown for the sake of illustrationin FIGS. 4 and 5, element 30 bears four strips, 34A, 34B, 34C, and 34D,each having its own,

individual input lead, respectively, 52A, 52B, 52C, and 52D. Now, it canbe assumed for example that only one arm of the U-shape of receptionelement bears two surface portions respectively identified in FIGS. 4and 5 as 28A and 28C registered with corresponding strips 34A and 34C.Element 20 is coupled to output lead 29. It will be seen from FIGS. 4and 5 that when shielding means 36 is in its normal position,electrically-conductive material of the body of the latter lies whollybetween portion 28A and strip 34A and between portion 24C and strip'34C.Shielding means 36, as shown, includes a pair of dielectric aperturesidentified respectively as 38A and 38C. The latter apertures aredisposed so that when shielding means 36 is moved to a switchingposition as shown in FIG. 4, the dielectric apertures then lierespectively between registered portions 28A and strip 34A andregistered portion 28C and strip 34C and therefore permit any changingpotential signal on only either strip 34C or 34A to be capacitivelycoupled to element 20. In order to insure that there is only one uniqueposition at which this can occur, inasmuch as there may be a pluralityof surface portions and corresponding dielectric apertures, portions 28and apertures 38 are disposed respectively on element 20 and shieldingmeans 36 such that no surface portions are regstered with any aperturein any other position of the shielding means. This caa be accomplishedby distributing the dielectric apertures on the shielding means alonglines perpendicular to the direction of motion of the latter so thatwhen the shielding means is moved in that direction, each dielectricaperture sweeps out a unique path with respect to the transmissonelement, and not more than one surface portion 28 lies within each suchunique path.

In the example given, it can further be assumed that each switch isintended to code a particular corresponding decimal numeral into itsbinary equivalent, and that the shielding means of the switch shown inFIGS. 4 and 5 bears or is identified by the decimal indicium 5. In suchcase, leads 52A-D respectively constitute inputs corresponding to thebinary 1, 2, 4 and 8 values. If now a changing potential is impressed insequence on leads 52A- D in order when the shielding means is in itspormal position where capacitive coupling occurs between surface portion28A and 28C and corresponding strips 34A and 34C and leads 52A-D arethen sequentially energized, the signals will only appear where couplingoccurs. Because these are respectively the binary 1 and 4 values, itwill be seen that the act of depressing the shield to its conductivecoupling position and then commutating the input leads automaticallyprovides the correct serial binary coded signal at the output terminalsof the switch, i.e. 0101. Where, as shown in FIGS. 1 and 2, there isessentially a double switching mechanism due to the trim arms of theU-shape of element 20 and shielding means 36, the output can be codedinto a number havng twice as many places as it can with but a singlepair of transmission and reception surfaces.

The configuration of the three basic elements is not particularlyimportant. For example, the surfaces can be curved, corrugated, or thelike, provided, of course, that there is a proper path allowed for themotion of the shielding means between the transmission and receptionelements and the latter are close enough to one another to permitcapacitive coupling. The number and placement of surface portions,dielectric apertures and receiving strips required depend, naturally,upon the particular encoding scheme used. For example, the switch can beused to convert demimal to serial bianry, to serial excess-three binary,to serial reflected binary, to select but a few of the many codesavailable. It will further be appreciated that while in the embodimentdescribed the electrostatic shielding means itself is movable, and thetransmission and reception elements are fixed, other embodiments can bemade in which the transmission element or the reception element ismovable while the other two 6 elements are fixed. However, theembodiment shown has a distinct advantage in that the movable element,being grounded, does not carry any substantial current when the switchis conducting, and this aspect constitutes a distinct safety feature.The provision of layers 24 and 26 insure that signals can only becoupled when the shield is in its transmitting position.

Because the switching means heretofore described is capable of providingdirect encoding, a multiple key keyboard can be readily formed using anumber of such switching means. Thus, there is shown in FIG. 6 asimplified schematic diagram of such a keyboard limited to two suchswitches for the sake of simplicity. The embodiment of FIG. '6 includesa source of changing potential, such as sinusoidal oscillator 52, andtwo switches shown generally at 54 and 56. The two switches are the samein that they all include (identified only in switch 54 as exemplary) areception element or bar 60, a shielding element or key 62, andplurality of four transmission elements or strips 64A, 64B, 64C and 64D.All of the transmission elements of the switches are connectable tooscillator 52 in sequence by commutating device '66, and all keys 62 aregrounded.

The two switches differ only in the number and position of dielectricapertures which are disposed in the respective shielding elements orkeys 62. For example, one can assume that the key 62 of switch 54 isidentified by or coded to represent the decimal numeral 3, key 62 ofswitch 56 being representative of the decimal numeral 4. The switchescan, for example, encode these demical numerals directly into serialbinary outputs while the appropriate keys are depressed. To encode asingle demical number in binary notation requires only four transmissionelements or strips. Key 62 of switch 54 will then include two aperturesintended to permit coupling of the signals sequentially applied tostrips 64A and 64B, representing binary l and binary 2, to the receptionbar. Key 62 of switch 56 will have but one aperture to permit thecorresponding 64C strip (representing binary 4) to be coupled to itsreception bar.

Input strips 64A are connected to one another, 64B are connected to oneanother, and so forth, so that the operation of commutating device 66results in all strips 64A, 64B, 64C and 64D being momentarily energizedand deenergized in sequence. All reception elements or bars 60 areelectrically connected to one another to provide a single output linewhich is fed to amplifier 68, and thence through a signal conditioningdevice 70 to some storage means such as shift register 72.

In operation, it will be seen that if key 62 of switch 54 is depressedto its operative position and commutator 66 turns, the latter firstconnects and then disconnects the output of oscillator 62 in sequence tostrips 64A, 64B, 64C and 64D. The successive signals imposed on strips64A and 64B will appear as pulses coupled in that order to the input ofamplifier 68; but because no apertures exist with respect .to srips 64Cand 64D, there will be an absence of signals for the commutation periodsof those strips. Thus, a sequential series of pulses and no pulses willbe produced representing 1100; this signal, in binary notation with theleast significant digit to the left (in reverse order), representsdecimal value 3. This signal, appropriately conditioned as by filtering,wave-shaping and the like for entry into digital equipment by the usualsignal conditioning device 70, can then be entered in serial form intoshift register 72 for storage.

Obviously, the embodiment described in FIG. 6 is highly simplified inthat no timing system is included. However, a variety of timing systemscan be employed with the basic concepts. For example, a typicalmodification of the spstem of FIG. 6 is shown in FIG. 7 wherein likenumerals indicate like parts. It will be seen in FIG. 7, particularly,that an additional channel or input strip 64R has been added to eachswitch and consequently each switch contains an additional correspondingoutput bar 60R (identified only in connection with one switch,considered exemplary). In such case, the shielding element or key 62 ineveryswitch includes an additional aperture positioned to couple eachinput strip 64R with its corresponding output bar 60R when the key is inoperative position. The outputs of all 60R strips are connected torespective inputs of AND gate 74 and also the respective inputs of ORgate 76. The output of AND gate 74 is connected through an inverteramplifier 78 to an input of AND gate 80, another input of the latterbeing connected to the output of OR gate 76. The output of OR gate 80 isconnected to a start control terminal 82 of commutator 66. Additionally,all of strips 64A to 64D inclusive are connected to inputs of OR gate84. The output of the latter is connected to timing control inputterminal 86 of shift register 72.

in the operation of the device of FIG. 7, commutator 66 will normallyconnect the output of oscillator 52 to input 64R. unless a key isdepressed to permit the signal onstrip 64R to be coupled to bar 60R,commutator 66 A will not initiate any additional switching signals.However,

when one or more keys are depressed so that a signal is sensed on anybar 60R, this signal is fed through OR gate 76 to an input of AND gate80. If more than one of the 60R bars are connected to the input of ANDgate 74, the latter will produce an inhibit signal which when invertedby inverter 78 disables gate 80 so as to prevent commutating device 66from starting a switching sequence. If, however, only one 60R bar isenergized, there will be no inhibit signal from gate 74 and inverter 78thus provides an enabling signal to gate 80 so that commutating device66 will then operate to sequentially switch or apply momentary signalsfrom oscillator 52 to bars 60A-64D in order. It will be seen that thissequence of signals is also fed by gate 84 to the control input terminal86 of shift register 72 so that for every sequential input signalimpressed on the input strips 64A to 64D, regardless of whether or notcoupling occurs, register 72 will shift appropriately thus insuring theproper serial spacing of output signals from the switches throughamplifier 68 and detector 70.

-It will be apparent to those skilled in the art that a large number ofmodifications can be made on the basic concept without departing fromthe scope of the invention. For example, each key can include aplurality of input strips and like plurality of output bars, andsimultaneous commutation provided for both input and output signals. Alarge number of other logical gating schemes can be employed to handlethe read, inhibit, and timing functions desirable in using a group ofswitches of the present invention in connection with a multiple keycontrol.

Since certain changes may be made in the above apparatus withoutdeparting from the scope of the invention herein involved it is intendedthat all matter contained in the above description or shown in theaccompanying drawing shall be interpreted in an illustrative and not ina limiting sense.

What is claimed is:

1. Device for switching a changing potential, comprising in combination;

transmitting means defining a surface having a number of discrete,spaced-apart, electrically conductive surface portions all connectablesequentially to the source of said potential;

receiver means defining a second surface spaced a fixed distance fromthe surface of said transmitting means, said second surface beingelectrically conductive; and electrically conductive shield means havingat least one dielectric aperture therein and being disposed within theinterspace between and spaced from both 'of said surfaces; said surfaceportions, elements and apertures being disposed witlrat least one ofsaid means being movable with respect to the others so that there is arelative and unique position of said means wherein each said aperture ispositioned to permit capacitive coupling to be effected between acorresponding one of said surface portions and said second surface, allother positions pf all of said means being such that said shieldprovides electrostatic shielding preventing capacitive coupling fromoccurring between any of said surface portions and said second surface.

2. A device for switching as defined in claim 1 wherein said shieldmeans is said one of said means, which is movable with respect to theothers, and including means for releasably maintaining said shield meansin one of said other positions.

3. A device for switching as defined in claim 1 including a thirdelectrically conductive surface positioned with respect to saidtransmitting means so one of said apertures can be positioned to effectcapacitive coupling with one of said surface portions whenever any othersurface portions is capacitively coupled through a correspondingaperture to said second surface.

4. Keyboard device for switching a changing potential comprising, incombination;

a plurality of switches each having transmitting means defining asurface having a number of discrete, spaced apart, electricallyconductive surface portions connectable to the source of said potential,and receiver .means defining a second and electrically conductivesurface spaced a fixed distance from the surface of said transmittingmeans;

means for sequentially connecting each of said surface portionsmomentarily to said source of potential;

each of said switches having an electrically conductive shield meansdisposed between and spaced from the respective surfaces of saidtransmitting and receiver means of said each switch, each of said shieldmeans having a number of apertures therethrough, the combination ofnumber and position of said apertures being unique for each of saidshield means;

for each of. said switches said surface portions, elements and aperturesbeing disposed with at least one of said means being movable withrespect to the others so that there is a relative and unique position ofsaid means wherein each said aperture is positioned to permit capacitivecoupling to be effected between a corresponding one of said surfaceportions and said second surface, all other positions of all of saidmeans being such that said shield provides electrostatic shieldingpreventing capacitive coupling from occurring between any of saidsurface portions and said second surface.

5. Keyboard device as defined in claim 4 wherein each of said secondsurfaces is electrically connected to one another so as to provide asingle output channel.

6. Keyboard device as defined in claim 4 wherein each of said thirdsurfaces are electrically connected through logical gating means so asto inhibit said means for sequentially connecting from operating unlesscapacitive coupling of any surface portion with its corresponding secondsurface is occurring in only one of said switches.

v References Cited UNITED STATES PATENTS 3,293,640 12/1966 Chalfin340-365 THOMAS B. HABECKER, Primary Examiner US. Cl. X.R.

